The invention relates to the incineration of waste and the removal of contaminants such as nitrogen oxides, sulfur oxides, particulates, acid gas, heavy metals and organic toxins that result from the incineration.
The invention advantageously combines enriching the aft used in combustion with gaseous oxygen in the incineration process while using ozone to oxidize contaminants found in the combustion waste gas stream.
Oxygen enrichment can improve both the thermal destruction of waste as well as increase throughput. However, oxygen enrichment is well known to increase nitrogen oxides formation in combustion processes. Environmental permits generally restrict an incineration facility from increasing throughput when it results in higher emissions. Ozone injection into an Air Pollution Control (APC) system for treating incineration exhaust enables effective nitrogen oxides removal along with other contaminants. The chemistry of nitrogen oxides oxidation with ozone is described in a number of patents such as U.S. Pat. Nos. 5,206,002; 5,985,223; 6,162,409; 6,649,132; and 7,303,735.
The incineration of chemical and hazardous waste is of increasing interest when alternative methods to treat wastes are prohibitively costly or no longer permitted. International treaties and United States environmental regulations have limited alternatives such as the dumping of waste or ineffective treatments before emitting to the atmosphere. Process industries that desire to reach peak production often undertake optimization and intensification exercises to maximize production and profits with relatively low marginal investment in capital.
These exercises will often result in an increase in the quantity of waste generated which may be beyond the capability of the already installed incineration system to handle. A new incineration system can be expensive and generally will attract stricter environmental scrutiny. Notwithstanding the need for incineration equipment, the control of contaminants, particularly nitrogen oxides in gas streams has always been challenging.
State of the art control of nitrogen oxides emissions in incineration is generally achieved by combustion modifications. There are typically two techniques used; low nitrogen oxides burners and combustion staging. Low nitrogen oxides burners lower the flame temperature thereby forming less nitrogen oxides. In combustion staging, in the primary stage the initial combustion is carried out with limited air present, thereby forming a fuel rich environment. This ensures the formation of a reducing zone immediately downstream of the primary combustion zone where nitrogen oxides are reduced by a high level of carbon monoxide being present in the combustion products. In the second stage of the process, secondary air is introduced to complete the oxidation of combustion products including the carbon monoxide with or without the addition of supplemental fuel. Ammonia may be injected to lower nitrogen oxides by the SNCR (selective non catalytic reduction) method. A higher end method for controlling nitrogen oxides for combusting processes is SCR (selective catalytic reduction). This is not a preferred method for treating incineration exhaust due to a variety of reasons including expensive capital costs and energy intensive configurations required to offer sustainable performance.
The practice of enriching air with gaseous oxygen for improving combustion processes in glass and metal furnaces is well known. Using oxygen enrichment in incineration is fairly uncommon. Oxygen enrichment can improve both the thermal destruction of waste as well as increase throughput. Oxygen enrichment, however, is well known to increase nitrogen oxides formation in combustion processes. Environmental permits generally restrict an incineration facility from increasing throughput when it results in higher emissions. Air pollution control systems fitted on incinerators can generally handle a higher load of other air pollutants such as sulfur oxides, particulates, acid gases such as HCl, HF, Cl2, heavy metals and organic toxins such as dioxins, furans and PCBs, without sacrificing performance while nitrogen oxides control remains difficult.
Incineration processes are under increased scrutiny due to concern about public health and the environment and will require superior flue gas cleanup before emission into the atmosphere particularly when throughput is enhanced.
The invention combines oxygen enrichment with ozone based control of contaminants. This process will allow for a higher throughput of waste gas streams emanating from the incineration unit while also lowering the emission of contaminants to the atmosphere. The oxygen requirement is a small increment of what is required for oxygen enrichment and can be delivered from the same oxygen supply system as that which supplies the ozone generator. By increasing throughput in the same equipment, the unit cost of waste processed can be lowered even with the supplemental cost of nitrogen oxides control.
The oxygen enrichment and ozone based nitrogen oxides removal offers the ability to debottleneck the incineration process at minimal capital investment; with the least interruption to production activity; involves minimal changes in processing equipment; provides robust and superior nitrogen oxides removal while reducing the unit cost of the waste disposed of.